Memory Safety: Zig's Approach vs Rust's Borrow Checker
A comparative analysis of memory safety strategies. We contrast Rust's compile-time formal verification with Zig's approach of explicit memory management and runtime defenses.
Memory safety is the critical requirement for modern systems programming. While Rust has popularized compile-time verification via the borrow checker, Zig demonstrates an alternative philosophy: explicit resource management paired with robust runtime defenses.
The Rust Model: Formal Verification
Rust guarantees memory safety (spatial and temporal) through a strict ownership and borrowing system enforced at compile time.
- Mechanism: The compiler tracks the lifetime of every reference. It forbids simultaneous mutable aliasing and ensures no reference outlives its owner.
- Trade-off: This rigor eliminates entire classes of bugs (e.g., Use-After-Free) but imposes significant cognitive load and architectural constraints. Data structures that require shared mutable state (like graphs or doubly-linked lists) become difficult to implement.
The Zig Model: Defense in Depth
Zig does not provide a mathematical proof of safety at compile time. Instead, it prioritizes explicitness and observability.
1. Explicit Allocation
Zig has no global allocator. Functions that require memory must accept an Allocator parameter. This makes hidden allocations impossible and forces the developer to consider memory lifecycle at the API level.
// The signature explicitly states that memory will be allocated
fn parseJson(allocator: Allocator, input: []const u8) !JsonValue { ... }2. Runtime Safety Checks
By default, Zig builds in Debug and ReleaseSafe modes include runtime checks for:
- Out-of-bounds array access.
- Integer overflow/underflow.
- Unreachable code execution.
- Use of undefined values.
In these modes, memory errors result in an immediate, safe crash with a stack trace, rather than undefined behavior (UB).
3. The General Purpose Allocator (GPA)
Zig’s standard library includes a debug-capable allocator that tracks allocations. Upon program termination, the deinit() method reports any memory leaks, essentially integrating leak detection into the standard development loop.
Comparative Analysis
The choice between Rust and Zig represents a choice between constraints and discipline.
- Rust is optimal for high-risk environments (cryptography, browser engines) where safety must be guaranteed mathematically, justifying the development friction.
- Zig is optimal for systems where performance, control, and simplicity are paramount (game engines, embedded tools). It empowers the developer to manage memory safely through tooling rather than restriction.